1. Field of the Invention
The present invention relates to an aluminum alloy for fins of heat exchangers such as of automobile radiators and evaporators, which is readily workable for a fin (or readily corrugated), and is less deformed by brazing heat, and yet has improved thermal conductivity after the brazing.
2. Related Background Art
A heat exchanger, such as a radiator for an automobile, is constructed, as shown in FIG. 2, by stacking a flattened tubes 3 being clad with a brazing metal on the surface thereof, and bare corrugated fins 1; attaching a header 4 to each side of the tubes 3 (FIG. 2 showing the upper side only); jointing them by brazing; and joining a tank 6 to the header by aid of a packing sheet 5. An evaporator for an automobile is constructed, as shown in FIG. 3, by stacking tube-constituting sheets 8 and 8' composed of brazing sheets for forming a coolant pathway 7 and 7' and bare corrugated fins 1 alternately, and jointing them by brazing.
The fins of such heat exchangers are made, for example, from a sheet of an alloy of JIS 3003, an aluminum-manganese type alloy, of about 0.1 mm thick. In the fin material, an element for making the potential of aluminum basic, such as zinc, tin, indium, and the like, is sometimes incorporated in order to attain a sacrificial effect for protecting the tube material for the coolant pathway from through-pitting corrosion caused by the air.
Such fin materials are required to have an appropriate strength at an ordinary temperature for working such as corrugation working and assemblage working of tube materials. The fin materials are usually exposed to a high temperature of 600.degree. C. or higher when they are brazed, so that the fin material may sometimes be deformed by stress given by the tubes and jigs because of the thinness thereof to result in core deformation, failure of brazing, and so on. Accordingly, the fin materials are required to have sufficient strength and sufficient sag resistance at the high temperature. Incidentally, a thin material constituted by H14 alloy of JIS 3003 has strength of approximately from 14 to 18 kg/mm.sup.2.
Recently, because of needs for more compactness and higher performance of heat exchangers, the fin materials are strongly desired to be made thinner and to have higher thermal conductivity. Since the cross-sectional area of the fin material for heat radiation comes to be less with less thickness of the fin, so that improvement is required for the thermal conductivity of the fin materials. Although JIS 3003 alloys can be made thin from the standpoint of the strength, the electric conductivity thereof is as low as 40% IACS owing to solid dissolution of the added manganese (about 1.1% by weight), and is at a lower level among aluminum alloys. Accordingly, the JIS 3003 alloys have been unsuitable for use for fin materials of higher performance.